New iminophosphonamide chromium(II) complexes as highly active polymer-free ethylene oligomerization catalysts

The reactions of the deprotonated form of cis-{[(µ-N)(t-Bu)]2PN(H)(o-OMeC6H4)]2} (a) with either CrCl2(THF)2 or CrCl3(THF)3 afforded the corresponding dimeric Cr(II) and monomeric Cr(III) complexes {cis-[(µ-N)(t-Bu)]2[PN(o-MeOC6H4)]2Cr}2 (1a) and cis-[(µ-N)(t-Bu)]2[PN-2-MeOC6H4]2CrCl (2a). By replacing the ligand’s o-OMeC6H4 groups with less-crowded CH2CH2N(i-Pr)2 functionalities and reacting the deprotonated form of cis-{[(µ-N)(t-Bu)]2[PN(H)CH2CH2N(i-Pr)2)]2} (b) with CrCl2(THF)2, the dimetallic, divalent {cis-[(µ-N)(t-Bu)]2[PNCH2CH2N(i-Pr)2)]2Cr}2 (1b) was obtained in crystalline form. Upon activation with MAO, both 1a and 1b afforded highly active, polyethylene-free ethylene oligomerization catalysts. Complex 2a is instead catalytically inactive